It is desirable in the medical profession to inject fluids such as liquid medicaments into the body of the patient, whether human or animal, at a relatively slow rate over a prolonged period of time. Several varieties of medical treatments such as chemotherapy, pre- and post-surgery treatments for the prevention of blood clotting, various nutrient treatments, various antibiotic treatments and treatment of certain other diseases generally required low rates of injection over a long period of time. Such injections are generally made intravenously or subcutaneously into the patient. Some of these treatments generally require that the fluid be introduced relatively continuously over an extended period of time at varying rates ranging from very slow rates, usually about 1 cc per 24-hour period, to relatively fast rates of more than about 5 cc per 24-hour period. Because a significant increase in the predetermined rate of injection during these continuous treatments must be accurately controlled to prevent serious injury to or fatality of the patient, the rate of injection must be frequently and closely monitored.
There are a number of liquid dispensing or injection devices presently known which attempt to dispense or inject a liquid into a patient at a very slow continuous rate over an extended period of time. These prior art injection systems, however, suffer from a number of drawbacks.
One problem frequently encountered with such prior art injection systems is that the system cannot reliably inject small quantities of fluid over a prolonged period of time. To compensate for this inadequacy, medical personnel have had to dilute the liquid medicament with neutral fluids to reduce the unit liquid medicament concentration of the fluid being injected so that a relatively large quantity of fluid could be injected without overdosing the patient with the active liquid medicament and so that the undesired consequences due to variations in fluid injection rate were minimized. This, of course, increases the weight of the fluid being injected and also increases the power required to inject this larger quantity of fluid into the patient. The net result is that the overall weight of these systems due to the weight of the fluid to be injected and the weight of the necessary power supply is at a level that virtually precluded these injection systems being made sufficiently portable for the patient to carry on his usual daily activities.
Another problem commonly found with the prior art injection systems is that a failure in some component of the system can cause the injection system to exceed the desired injection rate. This not only has resulted in the use of the diluted liquid medicament but has also required frequent monitoring of the injection system by medical personnel to compensate for this problem. To further compensate for this problem, the patient has usually been confined to a medical facility so that counteractive treatment is quickly available in the event of over-dosage of the patient.